A Prospective Study of Advanced Diagnostics in People With an Unclear Diagnosis of Cystic Fibrosis

Cystic Fibrosis (CF), CFTR-related Disorders

CFTR-related disorders, Advanced Diagnostics, Personalised medicine, Cystic Fibrosis (CF), Nasal potential difference (NPD), Intestinal current measurements (ICM), Organoids, Sweat chloride concentration (SCC)

Sometimes it is very difficult to tell if someone has cystic fibrosis (CF), especially when they have rare CF genes. Without this certainty, they are unlikely to get the correct treatment so their health may be affected. More accurate ways to test for CF are therefore needed in this situation. The aim of this study is to develop a more accurate test using what are called "organoids" or "mini organs." Organoids are grown in the laboratory from a small piece of gut tissue. As they have the person's exact genes, they can show if the CF gene ("CFTR") is working correctly or not and thus if the person has CF. The investigators will compare the organoid response with the current more established tests, such as the sweat test and CF genetics, and other recognised specialist tests called nasal potential difference (NPD) and intestinal current measurement (ICM). The gut tissue is usually taken by a quick, relatively painless, outpatient procedure (rectal biopsy). The additional benefit of organoids is that they can also help us to work out the best treatment for that individual by testing how well the gut tissue responds to different drugs in the laboratory. The investigators wish to carry out this research to prove that gut organoids are a better way to test for CF in this situation. The goal will be to diagnose people faster and for them to get better treatment quicker, both key for leading a longer and healthier life.

BACKGROUND The diagnosis of cystic fibrosis (CF) can be difficult in an important minority of individuals (\ 10-15% CF diagnoses), particularly when one or two rare variants of the CF gene (cystic fibrosis transmembrane conductance regulator; CFTR) are identified and the sweat test (sweat chloride concentration; SCC) is non-diagnostic. Biomarkers of CFTR function enable the quantification of individual CFTR protein function, the key underlying defect associated with CF. Such biomarkers play an important role in diagnosing CF and have the additional key capability of measuring the treatment benefits of CFTR targeting therapies, such as CFTR modulators. The currently validated biomarkers of CFTR function; such as SCC, nasal potential difference (NPD) and intestinal current measurements (ICM) can accurately characterise individuals at the extreme ranges of CFTR function (healthy and pancreatic insufficient (PI) CF), but are less reliable in intermediate ranges, particularly when clinical features are atypical. This 'difficult diagnosis' can lead to both a false positive and negative diagnostic outcome, with missed opportunities for the introduction of effective treatments, such as CFTR modulators. Some individuals remain undiagnosed for many years, even decades, so significant disease, associated with declining health, can occur. Individuals and their families are often frustrated and disillusioned by years of uncertainty. In addition, there is a group of individuals with a more limited phenotype (e.g. pancreatitis or congenital bilateral absence of the vas deferens, CBAVD), in whom the strict CF diagnostic criteria are not satisfied - their condition is termed CFTR-related disorder (RD). Recent European CF Society (ECFS) guidelines have highlighted an urgent need for a more accurate and streamlined pathway to their diagnosis. The Difficult CF Diagnosis (DCFD) service at the Royal Brompton Hospital (RBH) uses NPD, along with whole gene analysis of CFTR and other associated genes for diagnosing unclear cases. Intestinal current measurements (ICM) - the assessment of CFTR function in Ussing chambers using ex vivo tissue biopsies of the intestinal epithelium - is currently being set-up. It is well known that an important sub-group of patients remain undiagnosed. More recently, CFTR-dependent tests in patient-derived intestinal organoids (established at the Beekman lab, University Medical Center (UMC) Utrecht University, Utrecht, The Netherlands) were also found to have excellent diagnostic capabilities with the added benefits of providing key phenotyping and prognostic information, using two different techniques - forskolin-induced-swelling (FIS) and morphological analysis (e.g. steady state lumen area, SLA). These both rely on CFTR-dependent ion and fluid secretion into the organoid lumen. Organoids can also quantify individual responses to CFTR modulators in the laboratory for estimation of potential clinical benefit and can be biobanked for future studies. How one should optimally use these different biomarkers in the context of difficult-to-diagnose individuals and treatment thereof with CFTR modulators is unclear. ADVANCE-CFTR study is a prospective cohort study of 40-50 individuals with difficult-to-diagnose disease. The participants will be recruited from the Difficult CF Diagnosis (DCFD) service of the Royal Brompton Hospital. Up to 15 CF patients and 15 healthy (non-CFTR disease) controls will also be recruited to validate the tests and anchor extremes in the assays.

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